AWK(1) NetBSD General Commands Manual AWK(1)
NAMEawk -- pattern-directed scanning and processing language
SYNOPSISawk [-Ffs] [-vvar=value] [-safe] [-d[N]] [prog | -ffilename] file ...awk -versionDESCRIPTIONawk is the Bell Labs' implementation of the AWK programming language as
described in the The AWK Programming Language by A. V. Aho, B. W.
Kernighan, and P. J. Weinberger.
awk scans each input file for lines that match any of a set of patterns
specified literally in prog or in one or more files specified as -ffilename. With each pattern there can be an associated action that will
be performed when a line of a file matches the pattern. Each line is
matched against the pattern portion of every pattern-action statement;
the associated action is performed for each matched pattern. The file
name - means the standard input. Any file of the form var=value is
treated as an assignment, not a filename, and is executed at the time it
would have been opened if it were a filename.
The options are as follows:
-d[N] Set debug level to specified number N. If the number is omitted,
debug level is set to 1.
-ffilename
Read the AWK program source from specified file filename, instead
of the first command line argument. Multiple -f options may be
specified.
-Ffs Set the input field separator FS to the regular expression fs.
-mrNNN, -mfNNN
Obsolete, no longer needed options. Set limit on maximum record
or fields number.
-safe Potentially unsafe functions such as system() make the program
abort (with a warning message).
-vvar=value
Assign the value value to the variable var before prog is exe-
cuted. Any number of -v options may be present.
-version
Print awk version on standard output and exit.
An input line is normally made up of fields separated by white space, or
by regular expression FS. The fields are denoted $1, $2, ..., while $0
refers to the entire line. If FS is null, the input line is split into
one field per character.
A pattern-action statement has the form
pattern { action }
A missing { action } means print the line; a missing pattern always
matches. Pattern-action statements are separated by newlines or semi-
colons.
An action is a sequence of statements. Statements are terminated by
semicolons, newlines or right braces. An empty expression-list stands
for $0. String constants are quoted " ", with the usual C escapes recog-
nized within. Expressions take on string or numeric values as appropri-
ate, and are built using the Operators (see next subsection). Variables
may be scalars, array elements (denoted x[i]) or fields. Variables are
initialized to the null string. Array subscripts may be any string, not
necessarily numeric; this allows for a form of associative memory. Mul-
tiple subscripts such as [i,j,k] are permitted; the constituents are con-
catenated, separated by the value of SUBSEP.
Operatorsawk operators, in order of decreasing precedence, are:
(...) Grouping
$ Field reference
++ -- Increment and decrement, can be used either as postfix or prefix.
^ Exponentiation (the ** form is also supported, and **= for the
assignment operator).
+ - ! Unary plus, unary minus and logical negation.
* / % Multiplication, division and modulus.
+ - Addition and subtraction.
space String concatenation.
< ><= >=!= == Regular relational operators
~ !~ Regular expression match and not match
in Array membership
&& Logical AND
|| Logical OR
?: C conditional expression. This is used as expr1?expr2:expr3 .
If expr1 is true, the result value is expr2, otherwise it is
expr3. Only one of expr2 and expr3 is evaluated.
= += -=*= /= %= ^=
Assignment and Operator-Assignment
Control Statements
The control statements are as follows:
if (expression)statement [elsestatement]
while (expression)statementfor (expression;expression;expression)statementfor (varinarray)statementdostatementwhile (expression)breakcontinuedeletearray [expression]
deletearrayexit [expression] expressionreturn [expression]
{ [statement ...] }I/O Statements
The input/output statements are as follows:
close(expr)
Closes the file or pipe expr. Returns zero on success; otherwise
nonzero.
fflush(expr)
Flushes any buffered output for the file or pipe expr. Returns
zero on success; otherwise nonzero.
getline [var]
Set var (or $0 if var is not specified) to the next input record
from the current input file. getline returns 1 for a successful
input, 0 for end of file, and -1 for an error.
getline [var] <file
Set var (or $0 if var is not specified) to the next input record
from the specified file file.
expr| getline
Pipes the output of expr into getline; each call of getline
returns the next line of output from expr.
next Skip remaining patterns on this input line.
nextfile
Skip rest of this file, open next, start at top.
print [expr-list] [>file]
The print statement prints its arguments on the standard output
(or to a file if > file or to a pipe if | expr is present), sepa-
rated by the current output field separator OFS, and terminated
by the output record separator ORS. Both file and expr may be
literal names or parenthesized expressions; identical string val-
ues in different statements denote the same open file.
printfformat [,expr-list] [>file]
Format and print its expression list according to format. See
printf(3) for list of supported formats and their meaning.
Mathematical and Numeric Functions
AWK has the following mathematical and numerical functions built-in:
atan2(x, y)
Returns the arctangent of x/y in radians. See also atan2(3).
cos(expr)
Computes the cosine of expr, measured in radians. See also
cos(3).
exp(expr)
Computes the exponential value of the given argument expr. See
also exp(3).
int(expr)
Truncates expr to integer.
log(expr)
Computes the value of the natural logarithm of argument expr.
See also log(3).
rand() Returns random number between 0 and 1.
sin(expr)
Computes the sine of expr, measured in radians. See also sin(3).
sqrt(expr)
Computes the non-negative square root of expr. See also sqrt(3).
srand([expr])
Sets seed for random number generator ( rand()) and returns the
previous seed.
String Functions
AWK has the following string functions built-in:
gensub(r, s, h, [t])
Search the target string t for matches of the regular expression
r. If h is a string beginning with g or G, then replace all
matches of r with s. Otherwise, h is a number indicating which
match of r to replace. If no t is supplied, $0 is used instead.
Unlike sub() and gsub(), the modified string is returned as the
result of the function, and the original target is not changed.
Note that the \n sequences within replacement string s supported
by GNU awk are not supported at this moment.
gsub(r, s, [t])
Same as sub() except that all occurrences of the regular expres-
sion are replaced; sub() and gsub() return the number of replace-
ments.
index(s, t)
the position in s where the string t occurs, or 0 if it does not.
length([string])
the length of its argument taken as a string, or of $0 if no
argument.
match(s, r)
the position in s where the regular expression r occurs, or 0 if
it does not. The variables RSTART and RLENGTH are set to the
position and length of the matched string.
split(s, a, [fs])
splits the string s into array elements a[1], a[2], ..., a[n],
and returns n. The separation is done with the regular expres-
sion fs or with the field separator FS if fs is not given. An
empty string as field separator splits the string into one array
element per character.
sprintf(fmt, expr, ...)
Returns the string resulting from formatting expr according to
the printf(3) format fmt.
sub(r, s, [t])
substitutes s for the first occurrence of the regular expression
r in the target string t. If t is not given, $0 is used.
substr(s, m, [n])
Returns the at most n-character substring of s starting at posi-
tion m, counted from 1. If n is omitted, the rest of s is
returned.
tolower(str)
returns a copy of str with all upper-case characters translated
to their corresponding lower-case equivalents.
toupper(str)
returns a copy of str with all lower-case characters translated
to their corresponding upper-case equivalents.
Time Functions
This awk provides the following two functions for obtaining time stamps
and formatting them:
systime()
Returns the value of time in seconds since the start of Unix
Epoch (Midnight, January 1, 1970, Coordinated Universal Time).
See also time(3).
strftime([format [, timestamp]])
Formats the time timestamp according to the string format.
timestamp should be in same form as value returned by systime().
If timestamp is missing, current time is used. If format is
missing, a default format equivalent to the output of date(1)
would be used. See the specification of ANSI C strftime(3) for
the format conversions which are supported.
Other built-in functionssystem(cmd)
executes cmd and returns its exit status
Patterns
Patterns are arbitrary Boolean combinations (with ! || &&) of regular
expressions and relational expressions. Regular expressions are as in
egrep(1). Isolated regular expressions in a pattern apply to the entire
line. Regular expressions may also occur in relational expressions,
using the operators ~ and !~. / re / is a constant regular expression;
any string (constant or variable) may be used as a regular expression,
except in the position of an isolated regular expression in a pattern.
A pattern may consist of two patterns separated by a comma; in this case,
the action is performed for all lines from an occurrence of the first
pattern though an occurrence of the second.
A relational expression is one of the following:
expression matchop regular-expressionexpression relop expressionexpressioninarray-name
(expr, expr,...) inarray-name
where a relop is any of the six relational operators in C, and a matchop
is either ~ (matches) or !~ (does not match). A conditional is an arith-
metic expression, a relational expression, or a Boolean combination of
these.
The special patterns BEGIN and END may be used to capture control before
the first input line is read and after the last. BEGIN and END do not
combine with other patterns.
Built-in Variables
Variable names with special meanings:
ARGC argument count, assignable
ARGV argument array, assignable; non-null members are taken as
filenames
CONVFMT conversion format used when converting numbers (default
"%.6g")
ENVIRON array of environment variables; subscripts are names.
FILENAME the name of the current input file
FNR ordinal number of the current record in the current file
FS regular expression used to separate fields; also settable by
option -Ffs.
NF number of fields in the current record
NR ordinal number of the current record
OFMT output format for numbers (default "%.6g" )
OFS output field separator (default blank)
ORS output record separator (default newline)
RS input record separator (default newline)
RSTART Position of the first character matched by match(); 0 if not
match.
RLENGTH Length of the string matched by match(); -1 if no match.
SUBSEP separates multiple subscripts (default 034)
Functions
Functions may be defined (at the position of a pattern-action statement)
thus:
function foo(a, b, c) { ...; return x }
Parameters are passed by value if scalar and by reference if array name;
functions may be called recursively. Parameters are local to the func-
tion; all other variables are global. Thus local variables may be cre-
ated by providing excess parameters in the function definition.
EXAMPLESlength($0) > 72
Print lines longer than 72 characters.
{ print $2, $1 }
Print first two fields in opposite order.
BEGIN { FS = ",[ \t]*|[ \t]+" }{ print $2, $1 }
Same, with input fields separated by comma and/or blanks and
tabs.
{ s += $1 }END { print "sum is", s, " average is ", s/NR }
Add up first column, print sum and average.
/start/, /stop/
Print all lines between start/stop pairs.
BEGIN { # Simulate echo(1)for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]printf "\n"exit }SEE ALSOegrep(1), lex(1), sed(1), atan2(3), cos(3), exp(3), log(3), sin(3),
sqrt(3), strftime(3), time(3)
A. V. Aho, B. W. Kernighan, P. J. Weinberger, The AWK ProgrammingLanguage, Addison-Wesley, 1988. ISBN 0-201-07981-X
AWK Language Programming, Edition 1.0, published by the Free Software
Foundation, 1995
HISTORYnawk has been the default system awk since NetBSD 2.0, replacing the pre-
viously used GNU awk.
BUGS
There are no explicit conversions between numbers and strings. To force
an expression to be treated as a number add 0 to it; to force it to be
treated as a string concatenate "" to it.
The scope rules for variables in functions are a botch; the syntax is
worse.
NetBSD 7.0 April 6, 2015 NetBSD 7.0

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